Environmental conditions controlling Cold-water corals occurrence in western Melilla (western Mediterranean) since the last deglaciation.

Abstract

Cold-water coral (CWC) mounds are widely distributed in the eastern Alboran Sea (westernmost Mediterranean), specifically in the so-called East and West Melilla CWC mound provinces (EMCP, WMCP). Here we present a study on the environmental changes that occurred in the WMCP since the last deglaciation (~14 kyr BP), based on the analysis of the sediment core MD13-3451 (370 m water depth). The reconstructed palaeoceanographic changes allowed for the identification of diverse circulation patterns, which potentially influenced the life and demise of CWC communities in the WMCP. The analyses performed include sediment grain-size, geochemical measurements in foraminifera coating (U/Mn ratio) and calcite (stable isotopes, Mg/Ca-derived Deep Water Temperatures; DWTs), and the assessment of benthic foraminiferal species assemblages tolerating low-oxygen conditions (relative abundance of Globobulimina affinis). Furthermore, seawater δ18O (δ18Osw) and seawater δ18O corrected for the ice volume signal (δ18Ow-ivc) have been estimated via paired analyses of Mg/Ca and δ18Ocarbonate. Our findings suggest: i) the occurrence of pulses of relatively high DWTs, moderate to strong bottom water hydrodynamics and well-oxygenated waters favored a suitable environment for CWCs during the Early Holocene (EH), ii) a rapid freshening of the waters occurred during the EH, indicating major oceanographic changes. These results, when combined with available records from neighboring sites, reveal that such flourishing stage is closely coupled to a re-organization of the Alboran Sea water column structure. More precisely, the emergence of a newly formed water mass probably originated in the Gulf of Lion (northwestern WM) most likely replaced the older Levantine Intermediate Water (LIW) and might have also promoted the reactivation of CWC growth. Overall, our results highlight the crucial role of the Mediterranean circulation and stratification in controlling the temporal development of CWC mounds in the southern Alboran Sea, and also emphasize the importance of integrating a wide range of environmental variables and spatial scales when investigating these complex ecosystems.